Numerous items such as smart phones, smart watches, tablets, automobiles, aerial drones, appliances, aircraft, exercise aids, and game controllers may utilize motion sensors during their operation. In many applications, various types of motion sensors such as accelerometers and gyroscopes may be analyzed independently or together in order to determine varied information for particular applications. For example, gyroscopes and accelerometers may be used in gaming applications (e.g., smart phones or game controllers) to capture complex movements by a user, drones and other aircraft may determine orientation based on gyroscope measurements (e.g., roll, pitch, and yaw), and vehicles may utilize measurements for determining direction (e.g., for dead reckoning) and safety (e.g., to recognizing skid or roll-over conditions).
Many sensors such as accelerometers, gyroscopes, pressure sensors, and microphones are implemented as microelectromechanical systems (MEMS) sensors. Micromechanical components of the sensor are fashioned using silicon fabrication techniques, and those micromechanical components respond (e.g., move) in response to certain external stimuli that are measured by the sensor, based on the design of the particular micromechanical components. The response of the micromechanical component to the external stimuli may be measured, e.g., by utilizing the moving micromechanical component as a “moving electrode” and measuring a voltage change caused by the motion of the moving electrode relative to a “fixed electrode.” Based on the design of the sensor, this change in voltage is related to the parameter to be measured (e.g., acceleration, angular velocity, pressure, etc.) by a scaling factor.
In the case of a MEMS gyroscope, certain micromechanical components may have a drive mode resonant frequency and may be caused to vibrate at this frequency (i.e., a drive frequency). A number of components are often physically connected by a numerous springs, each of which is designed to enable motion in certain directions while restricting movement in other directions. When a mass that is vibrating at the drive frequency experiences a Coriolis force in a direction that is perpendicular to the drive direction as a result of rotation, it will move in this direction (e.g., a “sense” or “Coriolis” direction) at the drive frequency if springs or other structural features do not prevent such a motion. This motion may then be sensed based on the motion of the mass (or in some applications, an additional proof mass connected by additional springs) in the sense direction, e.g., based on the voltage change between a moving electrode on the mass and a fixed electrode. The rotation is measured based on the gain associated with the voltage change.
The mass or masses that make up a sense oscillator may have one or more sense mode resonant frequencies and a quality factor. The gain of the gyroscope may depend on the frequency at which movement is measured (e.g., relative to the sense mode resonant frequency) and the quality factor. If these parameters do not match the designed parameters (e.g., as a result of variances in manufacturing), the gain of the gyroscope may differ from an expected gain, which may result in measurement errors. As components wear over time, or if components are damaged, the gain of the gyroscope may change.